Heretofore, there has been known a piezoelectric MEMS (Micro Electro Mechanical Systems) vibrator in which an excitation portion including a piezoelectric thin film is formed on a single crystal Si layer.
For example, in the following Patent Document 1, a piezoelectric MEMS vibrator in which a piezoelectric thin film formed of scandium-containing aluminum nitride is provided on a Si single crystal has been disclosed. The piezoelectric MEMS vibrator described above has a so-called Cavity SOI (Silicon on insulator) structure in which a cavity portion is provided in a Si single crystal.
In addition, in the following Patent Document 2 and Non-Patent Documents 1 and 2, a piezoelectric MEMS vibrator in which a piezoelectric film layer formed of aluminum nitride is provided on a SOI substrate has also been disclosed.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2009-10926    Patent Document 2: U.S. Patent Application Publication No. 2010/0013360A1    Non-Patent Document 1: Procedia Chemistry1 (2009) 1395 to 1398    Non-Patent Document 2: Frequency Control Symposium, 2007, IEEE International 1210 to 1213